After predefined operating times, power unit components, particularly of heavy-duty power units such as turbine blades, produced in composite construction must be stripped down to the base material, to be able to subsequently recoat it for further use.
Conventionally, the coating is removed using wet chemical processes. The base materials of such turbine blades are nickel-based, cobalt-based and titanium-based alloys, while the coatings to be applied are made of corrosion-resistant nickel-aluminum alloys, nickel-chromium-aluminum alloys, MCrAlY alloys (M=nickel, cobalt, nickel-cobalt alloy or iron) or a platinum-aluminum alloy. When removing these coatings by wet chemical processes, the danger exists that upon reaching the base material, it will be partially removed or chemically attacked, because the base material and the coating are very similar in their chemical composition. An attack on the base material during coating removal using wet chemical processes is not even avoidable by process analytics, since the extent of unwanted surface removal is only determinable using measuring-technique measures after the stripping process has ended, so that it is necessary to restrict the frequency of coating removal when using these methods. Moreover, such wet chemical processes are ecologically dangerous. They require a high expenditure for the necessary occupational safety and health measures and the disposal of the process agents in a manner compatible with the environment.
It is an object of the present invention to provide a method and device that may strip such power unit components better and more precisely, while avoiding the wet chemical methods.